&pound;30.9m - the amount spent on unauthorised IAPs in Britain each month

Microsoft has calculated a truly staggering figure for the monthly spend on unauthorised apps and in-app purchases in the UK.

The Guardian has word of a Microsoft survey that pegs the number at an eye-watering 30.9m.

It gathered this data by questioning 2,000 British parents who own a smartphone or tablet, 28 per cent of which claim their kids had made purchases without permission. 83 per cent said they had suffered from bill shock” – that is, noticing unexpected payments on their bank statement.

Those questioned reckoned these surprise bills reached an average of 34.18.

77 per cent believed that parents need more help from tech firms to keep control of their kids' app habits.

Of course, you'd hope that those who were stung once took steps to prevent it happening again, suggesting that even if true that monthly number is unlikely to persevere.

Microsoft commissioned the survey to help promote its Kid's Corner functionality in Windows Phone 8.